On Tuesday, May 07, 2013 12:59:45 PM Vasilis Liaskovitis wrote:
> Hi,
>
> On Tue, May 07, 2013 at 02:59:05AM +0200, Rafael J. Wysocki wrote:
> > On Monday, May 06, 2013 06:28:12 PM Vasilis Liaskovitis wrote:
> > > On Sat, May 04, 2013 at 01:21:16PM +0200, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > >
> > > > Introduce .offline() and .online() callbacks for memory_subsys
> > > > that will allow the generic device_offline() and device_online()
> > > > to be used with device objects representing memory blocks. That,
> > > > in turn, allows the ACPI subsystem to use device_offline() to put
> > > > removable memory blocks offline, if possible, before removing
> > > > memory modules holding them.
> > > >
> > > > The 'online' sysfs attribute of memory block devices will attempt to
> > > > put them offline if 0 is written to it and will attempt to apply the
> > > > previously used online type when onlining them (i.e. when 1 is
> > > > written to it).
> > > >
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > > ---
> > > > drivers/base/memory.c | 105 +++++++++++++++++++++++++++++++++++++------------
> > > > include/linux/memory.h | 1
> > > > 2 files changed, 81 insertions(+), 25 deletions(-)
> > > >
> > > [...]
> > >
> > > > @@ -686,10 +735,16 @@ int offline_memory_block(struct memory_b
> > > > {
> > > > int ret = 0;
> > > >
> > > > + lock_device_hotplug();
> > > > mutex_lock(&mem->state_mutex);
> > > > - if (mem->state != MEM_OFFLINE)
> > > > - ret = __memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE, -1);
> > > > + if (mem->state != MEM_OFFLINE) {
> > > > + ret = __memory_block_change_state_uevent(mem, MEM_OFFLINE,
> > > > + MEM_ONLINE, -1);
> > > > + if (!ret)
> > > > + mem->dev.offline = true;
> > > > + }
> > > > mutex_unlock(&mem->state_mutex);
> > > > + unlock_device_hotplug();
> > >
> > > (Testing with qemu...)
> >
> > Thanks!
> >
> > > offline_memory_block is called from remove_memory, which in turn is called from
> > > acpi_memory_device_remove (detach operation) during acpi_bus_trim. We already
> > > hold the device_hotplug lock when we trim (acpi_scan_hot_remove), so we
> > > don't need to lock/unlock_device_hotplug in offline_memory_block.
> >
> > Indeed.
> >
> > First, it looks like offline_memory_block_cb() is the only place calling
> > offline_memory_block(), is that right? I'm wondering if it would make
>
> correct.
Great!
> > sense to use device_offline() in there and remove offline_memory_block()
> > entirely?
>
> possibly. Not sure if we can get hold of the struct device from
> mm/memory_hotplug.c, maybe we still need the helper function that operates
> directly on the memory block.
We can pass mem->dev to device_offline() and the locking should be fine.
> > Second, if you ran into this issue during testing, that would mean that patch
> > [1/2] actually worked for you, which would be nice. :-) Was that really the
> > case?
>
> yes, the patchset works fine once the extra lock/unlock_device_hotplug is
> removed. For various dimm hot-remove operations, I saw either successfull
> offlining and removal, or failed offlining and aborted removal.
> You can add this to 1/2 (or, once the extra lock is removed, to 2/2 as well):
>
> Tested-by: Vasilis Liaskovitis <vasilis.liaskovitis@xxxxxxxxxxxxxxxx>
Thanks!
Updated patch is appended for completness.
> >
> > > A more general issue is that there are now two memory offlining efforts:
> > >
> > > 1) from acpi_bus_offline_companions during device offline
> > > 2) from mm: remove_memory during device detach (offline_memory_block_cb)
> > >
> > > The 2nd is only called if the device offline operation was already succesful, so
> > > it seems ineffective or redundant now, at least for x86_64/acpi_memhotplug machine
> > > (unless the blocks were re-onlined in between).
> >
> > Sure, and that should be OK for now. Changing the detach behavior is not
> > essential from the patch [2/2] perspective, we can do it later.
>
> yes, ok.
>
> >
> > > On the other hand, the 2nd effort has some more intelligence in offlining, as it
> > > tries to offline twice in the precense of memcg, see commits df3e1b91 or
> > > reworked 0baeab16. Maybe we need to consolidate the logic.
> >
> > Hmm. Perhaps it would make sense to implement that logic in
> > memory_subsys_offline(), then?
>
> the logic tries to offline the memory blocks of the device twice, because the
> first memory block might be storing information for the subsequent memblocks.
>
> memory_subsys_offline operates on one memory block at a time. Perhaps we can get
> the same effect if we do an acpi_walk of acpi_bus_offline_companions twice in
> acpi_scan_hot_remove but it's probably not a good idea, since that would
> affect non-memory devices as well.
>
> I am not sure how important this intelligence is in practice (I am not using
> mem cgroups in my guest kernel tests yet). Maybe Wen (original author) has
> more details on 2-pass offlining effectiveness.
OK
It may be added in a separate patch in any case.
> > > remove_memory is called from device_detach, during trim that can't fail, so it
> > > should not fail. However this function can still fail in 2 cases:
> > > - offline_memory_block_cb
> > > - is_memblock_offlined_cb
> > > in the case of re-onlined memblocks in between device-offline and device detach.
> > > This seems possible I think, since we do not hold lock_memory_hotplug for the
> > > duration of the hot-remove operation.
> >
> > But we do hold device_hotplug_lock, so every code path that may race with
> > acpi_scan_hot_remove() needs to take device_hotplug_lock as well. Now,
> > question is whether or not there are any code paths like that calling one of
> > the two functions above without holding device_hotplug_lock?
>
> I think you are right. The other code path I had in mind was userspace initiated
> online/offline operations from store_mem_state in drivers/base/memory.c. But we
> also do lock_device_hotplug in that case too. So it seems safe. If I find
> something else with stress testing the paths simultaneously (or another code
> path) I 'll update.
OK
Thanks,
Rafael
---
From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Subject: Driver core: Introduce offline/online callbacks for memory blocks
Introduce .offline() and .online() callbacks for memory_subsys
that will allow the generic device_offline() and device_online()
to be used with device objects representing memory blocks. That,
in turn, allows the ACPI subsystem to use device_offline() to put
removable memory blocks offline, if possible, before removing
memory modules holding them.
The 'online' sysfs attribute of memory block devices will attempt to
put them offline if 0 is written to it and will attempt to apply the
previously used online type when onlining them (i.e. when 1 is
written to it).
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Tested-by: Vasilis Liaskovitis <vasilis.liaskovitis@xxxxxxxxxxxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/base/memory.c | 105 +++++++++++++++++++++++++++++++++++++------------
include/linux/memory.h | 1
2 files changed, 81 insertions(+), 25 deletions(-)
Index: linux-pm/drivers/base/memory.c
===================================================================
--- linux-pm.orig/drivers/base/memory.c
+++ linux-pm/drivers/base/memory.c
@@ -37,9 +37,14 @@ static inline int base_memory_block_id(i
return section_nr / sections_per_block;
}
+static int memory_subsys_online(struct device *dev);
+static int memory_subsys_offline(struct device *dev);
+
static struct bus_type memory_subsys = {
.name = MEMORY_CLASS_NAME,
.dev_name = MEMORY_CLASS_NAME,
+ .online = memory_subsys_online,
+ .offline = memory_subsys_offline,
};
static BLOCKING_NOTIFIER_HEAD(memory_chain);
@@ -278,33 +283,64 @@ static int __memory_block_change_state(s
{
int ret = 0;
- if (mem->state != from_state_req) {
- ret = -EINVAL;
- goto out;
- }
+ if (mem->state != from_state_req)
+ return -EINVAL;
if (to_state == MEM_OFFLINE)
mem->state = MEM_GOING_OFFLINE;
ret = memory_block_action(mem->start_section_nr, to_state, online_type);
-
if (ret) {
mem->state = from_state_req;
- goto out;
+ } else {
+ mem->state = to_state;
+ if (to_state == MEM_ONLINE)
+ mem->last_online = online_type;
}
+ return ret;
+}
- mem->state = to_state;
- switch (mem->state) {
- case MEM_OFFLINE:
- kobject_uevent(&mem->dev.kobj, KOBJ_OFFLINE);
- break;
- case MEM_ONLINE:
- kobject_uevent(&mem->dev.kobj, KOBJ_ONLINE);
- break;
- default:
- break;
+static int memory_subsys_online(struct device *dev)
+{
+ struct memory_block *mem = container_of(dev, struct memory_block, dev);
+ int ret;
+
+ mutex_lock(&mem->state_mutex);
+ ret = __memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE,
+ mem->last_online);
+ mutex_unlock(&mem->state_mutex);
+ return ret;
+}
+
+static int memory_subsys_offline(struct device *dev)
+{
+ struct memory_block *mem = container_of(dev, struct memory_block, dev);
+ int ret;
+
+ mutex_lock(&mem->state_mutex);
+ ret = __memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE, -1);
+ mutex_unlock(&mem->state_mutex);
+ return ret;
+}
+
+static int __memory_block_change_state_uevent(struct memory_block *mem,
+ unsigned long to_state, unsigned long from_state_req,
+ int online_type)
+{
+ int ret = __memory_block_change_state(mem, to_state, from_state_req,
+ online_type);
+ if (!ret) {
+ switch (mem->state) {
+ case MEM_OFFLINE:
+ kobject_uevent(&mem->dev.kobj, KOBJ_OFFLINE);
+ break;
+ case MEM_ONLINE:
+ kobject_uevent(&mem->dev.kobj, KOBJ_ONLINE);
+ break;
+ default:
+ break;
+ }
}
-out:
return ret;
}
@@ -315,8 +351,8 @@ static int memory_block_change_state(str
int ret;
mutex_lock(&mem->state_mutex);
- ret = __memory_block_change_state(mem, to_state, from_state_req,
- online_type);
+ ret = __memory_block_change_state_uevent(mem, to_state, from_state_req,
+ online_type);
mutex_unlock(&mem->state_mutex);
return ret;
@@ -326,22 +362,34 @@ store_mem_state(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
struct memory_block *mem;
+ bool offline;
int ret = -EINVAL;
mem = container_of(dev, struct memory_block, dev);
- if (!strncmp(buf, "online_kernel", min_t(int, count, 13)))
+ lock_device_hotplug();
+
+ if (!strncmp(buf, "online_kernel", min_t(int, count, 13))) {
+ offline = false;
ret = memory_block_change_state(mem, MEM_ONLINE,
MEM_OFFLINE, ONLINE_KERNEL);
- else if (!strncmp(buf, "online_movable", min_t(int, count, 14)))
+ } else if (!strncmp(buf, "online_movable", min_t(int, count, 14))) {
+ offline = false;
ret = memory_block_change_state(mem, MEM_ONLINE,
MEM_OFFLINE, ONLINE_MOVABLE);
- else if (!strncmp(buf, "online", min_t(int, count, 6)))
+ } else if (!strncmp(buf, "online", min_t(int, count, 6))) {
+ offline = false;
ret = memory_block_change_state(mem, MEM_ONLINE,
MEM_OFFLINE, ONLINE_KEEP);
- else if(!strncmp(buf, "offline", min_t(int, count, 7)))
+ } else if(!strncmp(buf, "offline", min_t(int, count, 7))) {
+ offline = true;
ret = memory_block_change_state(mem, MEM_OFFLINE,
MEM_ONLINE, -1);
+ }
+ if (!ret)
+ dev->offline = offline;
+
+ unlock_device_hotplug();
if (ret)
return ret;
@@ -563,6 +611,7 @@ static int init_memory_block(struct memo
base_memory_block_id(scn_nr) * sections_per_block;
mem->end_section_nr = mem->start_section_nr + sections_per_block - 1;
mem->state = state;
+ mem->last_online = ONLINE_KEEP;
mem->section_count++;
mutex_init(&mem->state_mutex);
start_pfn = section_nr_to_pfn(mem->start_section_nr);
@@ -681,14 +730,20 @@ int unregister_memory_section(struct mem
/*
* offline one memory block. If the memory block has been offlined, do nothing.
+ *
+ * Call under device_hotplug_lock.
*/
int offline_memory_block(struct memory_block *mem)
{
int ret = 0;
mutex_lock(&mem->state_mutex);
- if (mem->state != MEM_OFFLINE)
- ret = __memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE, -1);
+ if (mem->state != MEM_OFFLINE) {
+ ret = __memory_block_change_state_uevent(mem, MEM_OFFLINE,
+ MEM_ONLINE, -1);
+ if (!ret)
+ mem->dev.offline = true;
+ }
mutex_unlock(&mem->state_mutex);
return ret;
Index: linux-pm/include/linux/memory.h
===================================================================
--- linux-pm.orig/include/linux/memory.h
+++ linux-pm/include/linux/memory.h
@@ -26,6 +26,7 @@ struct memory_block {
unsigned long start_section_nr;
unsigned long end_section_nr;
unsigned long state;
+ int last_online;
int section_count;
/*
--
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